"I feel that, in a dictatorship, if you want to be a person with dignity, if you want to be an honest person, you must fight for human rights and fight for freedom of speech," the writer and activist said in a 2007 interview. "Going to prison is part of that, and I have nothing to complain about."

Unwitting martyr

"Whether it was gross negligence or political murder, they have committed an unprecedented crime as no other government of the world had ever seen a Nobel Peace Prize laureate die in its custody," said Hu Jia, a leading Chinese human rights activist, when Liu first left jail.

Hu has known Liu's wife, Liu Xia, for years and served prison terms for his own advocacy.

Liu was first jailed for his role in the 1989 pro-democracy movement after the bloody crackdown in Beijing's Tiananmen Square -- and later for petitioning for political reform and co-writing a paper on policy toward Taiwan that was at odds with the government stance.

His most recent conviction, in December 2009, stemmed from his co-authorship of Charter 08, a manifesto calling for political reform and human rights in China. He received a surprisingly harsh 11-year prison term for "inciting subversion of state power."

In October 2010, while serving his sentence at Jinzhou Prison, near Shenyang, Liu was named the winner of the Nobel Peace Prize for "his long and non-violent struggle for fundamental human rights in China."

Liu's wife tweeted at the time that, upon hearing the news from her during a prison visit, her husband started to cry and said: "This is for the martyrs of Tiananmen Square."

"His continued effort throughout these 20 years has not changed society, but he's influenced a lot of people," Liu Xia, who married Liu Xiaobo in 1996 while he was serving an earlier prison sentence, told CNN in 2009.

"More people share his views and more people are fearless -- I believe that's what makes his effort worthwhile."

Photos:1989 Tiananmen Square crackdown

Timeline: Tiananmen Square crackdown – Ousted General Secretary of the Communist Party, Hu Yaobang, dies at age 73 on April 15, 1989. The next day, thousands of students gather at Tiananmen Square to mourn him -- Hu had become a symbol of reform for the student movement. A week later thousands more marched to Tiananmen Square -- the start of an occupation that would end in a tragic showdown.

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Photos:1989 Tiananmen Square crackdown

Nil by mouth – May 13, 1989, student demonstrations at Tiananmen Square escalate into a hunger strike with thousands taking part and calling for democratic reforms.

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Photos:1989 Tiananmen Square crackdown

Tiananmen sit in – Student hunger strikers camp out on top of buses parked at Tiananmen Square.

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Photos:1989 Tiananmen Square crackdown

Gorbachev visits – May 16, 1989, then Chinese President Deng Xiaoping (center) takes then Soviet President Mikhail Gorbachev and his wife Raisa by the hand at the Great Hall of the People. Gorbachev's visit coincided with the student hunger strikes, forcing the official reception to be moved from Tiananmen Square to the airport -- embarrassing for the Chinese leadership.

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Price of protest – May 17, 1989: Five days in and the hunger strike begins to take its toll on students. Paramedics evacuate ailing protestors from the square.

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Photos:1989 Tiananmen Square crackdown

Witness to discontent – May 18, 1989 and Gorbachev has been in China for three days, witnessing street protests for each of those days. At the height of demonstrations, a million people were marching through Beijing.

Martial law – May 19, 1989, the sixth day of hunger strikes. Communist Party General Secretary Zhao Ziyang arrives at Tiananmen Square to address the students. He begins his now-famous speech by saying: "Students, we came too late. We are sorry." The next day, Premiere Li Peng declares martial law in parts of Beijing.

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Photos:1989 Tiananmen Square crackdown

Student-teacher relations – May 20, 1989, teachers from Beijing Normal University arrive at Tiananmen Square by the truckload to support their students after martial law was declared.

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Victory sign – May 20, 1989, pro-democracy demonstrators raise their fists and flash the victory sign while stopping a military truck filled with soldiers on its way to Tiananmen Square.

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Photos:1989 Tiananmen Square crackdown

Monument to Heroes – May 30, 1989, students from the Central Academy of Fine Arts create a 10-meter-tall statue of the Goddess of Democracy to boost morale amongst student protestors in Tiananmen Square. Erected in just four days, the statue was unveiled in front of the Monument to the People's Heroes.

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Mass protest – This photo was taken on June 2, 1989, showing hundreds of thousands gathered around the Goddess of Democracy.

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Troop movements – Countdown to the crackdown: Unarmed troops first approached Tiananmen Square on June 2.

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Crackdown – On the night of June 3 and into the early hours of June 4, armed troops and tanks moved in on students and other civilians in the areas around Tiananmen Square, opening fire on the crowds.

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Caught in the middle – June 4, 1989, journalists covering the crackdown were caught in the line of fire.

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Students fight back – June 4, 1989, students set fire to tanks. An official death toll has not been released but witnesses and human rights groups say hundreds were killed in the clash.

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Punishment – In the weeks following June 4, activists who were directly or indirectly involved in the pro-democracy demonstrations were arrested.

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Hong Kong vigil – Today, Hong Kong is the only Chinese territory where commemoration of the June 4 crackdown is allowed. Here, pro-democracy legislator Lee Cheuk-yan (left) unwraps a replica of the Goddess of Democracy at Hong Kong's June 4 Museum that opened on April 24, 2014.

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A pro-democracy group takes part in a rally outside the June 4 Museum on its opening day. A candlelight vigil commemorating the martyrs of the 1989 crackdown is held in the city's Victoria Park each year on June 4, attended by thousands.

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An infuriated Beijing tried to block the news of Liu's Nobel win and boycott the award, insisting that he was a common criminal and the prize was nothing more than a Western plot against China.

Despite China's refusal to let Liu or a representative travel to accept the award, the Nobel ceremony organizers placed his citation and medal on an empty chair in a poignant event in December 2010 in Oslo, Norway.

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"The passion he put into the way he was teaching -- even somebody like me, who had this kind of a language barrier on my first day, was able to appreciate how inspired and how excited the rest of the class was," recalled Ilaria Maria Sala, an Italian student of Liu's who stayed in touch with him over the years.

Armed with a doctoral degree in Chinese literature, Liu was a rising-star literary critic in the 1980s. He spent time in the United States and Europe as a visiting scholar, and turned his attention to the fight for democracy and human rights back home.

Having published numerous books on political and literary subjects overseas, Liu helped found the Chinese PEN Center, a literary and human rights organization. He later was on its board of directors in the 2000s.

'Forced to live in purgatory'

As Liu remained behind bars until recently, his wife -- an artist and a poet -- has paid a heavy price since his Nobel victory.

China put her under house arrest, rounded up Liu's supporters and froze diplomatic relations with Norway shortly after his peace prize win.

With her communication with the outside world almost completely cut by the government, Liu Xia has been suffering severe depression, according to friends, especially after authorities sentenced her brother to 11 years in prison over what supporters call trumped-up charges of business fraud.

"She didn't choose this life, but she'd been forced to live in purgatory," said Hu, the activist.

As for his own fate, Liu Xiaobo predicted that any Chinese Nobel Peace Prize winner would end up like Russian physicist and Soviet dissident Andrei Sakharov -- who received the prize in 1975.

"If China also has a dissident who becomes a Nobel Peace Prize laureate, it will be a big problem for the Chinese government," he told CNN in an interview in 2002 -- nearly eight years before receiving the award. "They can't imprison a Nobel laureate forever."